TheSamba.com :: View topic - High wattage H4 headlights + stock wiring

Tue May 03, 2016 12:14 pm

About a year ago, I upgraded my stock headlights to the Hella E-Code H4 units sold by BusDepot. I also installed 90/100W H4 bulbs.

GoWesty also sells high-wattage H4 bulbs. Based on the information on the page for their 80/100W H4 bulbs, I made no wiring changes and installed no relay because the GoWesty page states: Quote: DO NOT install in 80-85 Vanagon without upgraded wiring and relay with the kit found here.

1968-1979 buses are equipped to handle this wattage without modification.

Recently though, I've come across some older posts by people who I consider to be knowledgeable here saying that the 72+ buses should in fact use a relay with higher-than-stock wattage bulbs, as the power for the headlights runs through the ignition switch. I'm consequently a bit concerned about the reliability of my setup.

I've looked at the wiring diagram, and I'm confused as to why this is an issue. Two bulbs putting out 100W each, at 14.5v, is just under 14A load total, or 7A per bulb.

The weakest link seems to be the 2.5 sq mm wiring from the ignition switch to the light switch. Rounding down though, 2 sq mm wiring is equivalent to 14ga. 14ga wire should be able to carry 20 amps for up to 6 feet with less than 3% voltage drop (ref: Blue Sea Wire Selection Chart)

The headlights are each fused with 8A fuses. If fuses are rated to protect the wiring that is connected to them, and the 14ga+ equivalent wiring is rated for 20A (above the combined 16A possible draw), then what is the cause for concern over the ignition switch or the light switch? Why would either of these be rated below the fuses on the circuits beyond them? Are there cases of melted-down ignition switches and light switches?

I'm new to ACVWs, so I honestly don't know. I'm just looking for some information to substantiate the conjecture about the stock system not being up to par before I run wiring, install relays, etc.

Thanks!

Zach

Tue May 03, 2016 12:38 pm

Use the relays to provide adequate power to the bulbs without melting the light switch.

Tue May 03, 2016 1:18 pm

Randy in Maine wrote: Use the relays to provide adequate power to the bulbs without melting the light switch.

Any compelling reason to not run full amperage through the dimmer relay?

(This one is presumably rated for the bulbs in question)

It would be pretty convenient to install a standard 30/40A relay in a free socket in the stock fuse box, use power from the light switch to trigger the new relay, and have that relay switch fused power from the battery to pin 56 on the dimmer relay. This takes the load off the light switch, ignition switch, preserves the existing fuse locations, and doesn't muck with the stock wiring too much.

I've seen others adding two relays, inline fuses, etc. That seems to over-complicate things.

Thoughts?

Zach

Tue May 03, 2016 6:32 pm

that relay is rate for 150...you have (2) 100W bulbs...where are you going to find the extra 50w?

Tue May 03, 2016 6:38 pm

Quote: I've seen others adding two relays, inline fuses, etc. That seems to over-complicate things.
I found it simpler to run one relay for the low beams and one for the high There is space in the fuse box to hold both relays. All the wiring is the same except instead of the "power" from the dimmer relay supplying the appropriate (low beam/high beam) supply side of the fuse box, it gets redirected to control one or the other new relays. The supply side of the relay gets power from the a new fat wire from the positive side of the starter motor. I cant recall whether I ran that new fat wire through the supply side of the fuse box through the fuse then into the relays and out to the lights or directly into the relays that then went through the fuse box and out to the lights.

Now the ignition switch, headlight switch AND dimmer relay pathway is only operating with low amps (with respect to the lights) to flip the relays while the high amperage is handled by the relays. I even went and double wired the front lamps by installing a second headlamp wiring harness but i'm using 135w/90w bulbs and had more time on my hand back when I did all of this work :D Prior to this wiring modification there were times when the dimmer relay would stop working due to the excessive amperage passing through it. Since I've done this everything (related to the front headlamps) has been working flawlessly

Tue May 03, 2016 6:42 pm

skills@eurocarsplus wrote: that relay is rate for 150...you have (2) 100W bulbs...where are you going to find the extra 50w?

It says "2x150w" which I took to mean 300w total. So maybe I can buy those 135w high beams now. :lol:

Tue May 03, 2016 11:40 pm

Because the steady-state load current of 90 watt headlight bulbs is around 7.5 amps / bulb and the fuse is 8 amps, there would seem to be some margin.

There isn't.

The issue is the start-up current that occurs when the lamps are first lit. For a short time, the current is many many times the normal 7.5 amps operating current. What is saving you is (1) the resistance of the stock wiring, (2) a slow blowing fuse, and (3) the half dozen connections and switch / relay contacts the current must pass through between the battery and the lamps. In a way, this is good, because without all that loss, the surge current would be huge, and surge current is what causes the bulb filaments to burn out (and switch and relay contacts to burn or stick). [Ever notice that lamps usually fail when first turned on?] Thus, by luck, your lamps have a psuedo-soft-start circuit with the stock wiring.

Now here comes the dilemma: by adding buffering relays and heavier wiring, you take the load off of the headlight switch and high-beam relay - a good thing. But you also increase the surge current to the lamps, which is hard on the bulbs every time you turn them on - not such a good thing.

I recommend a compromise: install the relays, but don't get crazy with the wire size. Use wire just big enough to handle the steady-state operating current, which will still leave enough resistance to limit the turn-on surge current.

If I ever get a round 'tuit I'm going to look into what it would take to build a soft-start circuit that will limit the turn-on surge current, but otherwise allow full operating power to high-wattage lamps.

Wed May 04, 2016 3:35 am

Thank you for the excellent information, gentlemen. At the very least, it seems the dimming relay is undersized for the larger bulbs. (Skills - That is 150w per side of the relay, and each side feeds two bulbs. So you're right about lacking 50w of capacity.) And who knows about the switches.

I'll run a new 12ga wire from the starter and feed two new relays, which I'll install in the empty spaces in stock fuse box. I'll use the feed from the dimming relay to trigger each, and run the load side to the existing fuses.

I've read of people replacing the wiring to the bulbs with larger gauge. But I think you've given good reason to not, Telford (especially considering the stock wiring can handle 20a and only has to feed one bulb.

Telford, I did some brief reading on inrush current limiting devices. Looks like it would be somewhat simple to achieve, with a thermistor and triac (and an SCR). I think I'll just carry a couple of spare headlight bulbs though. But if you ever wire something up, let me know. I'd be interested in taking a look.

I'll report back after I finish up my wiring. Thanks again for all of the info!

Zach

Wed May 04, 2016 9:15 am

zh007 wrote: I did some brief reading on inrush current limiting devices. Looks like it would be somewhat simple to achieve, with a thermistor and triac (and an SCR).
Normally, yes. But in this case, the currents involved are large (15 amps or better because of driving two bulbs), and device voltage drops are significant. A triac or SCR would have a voltage drop of at least 0.7 volts or better when on (no biggie at household line voltages, not so at 12 volts). Maybe a big mosfet would work. Or maybe just a low value series resistor which gets shunted by a relay after a time delay?

And you would have to build two of them, one for low beam and one for high beam, so they would work when switching beams. Gets complex fast...

Wed May 04, 2016 7:48 pm

my understanding is

From discussion with D Stern, "Originals that came with bus were 6014, 60/50w (high/low beam) at 12.8v."